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From: Robin Murphy <robin.murphy@arm.com>
To: David Stevens <stevensd@chromium.org>, Christoph Hellwig <hch@lst.de>
Cc: Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
	Lu Baolu <baolu.lu@linux.intel.com>, Tom Murphy <murphyt7@tcd.ie>,
	iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 3/7] dma-iommu: skip extra sync during unmap w/swiotlb
Date: Thu, 19 Aug 2021 09:59:47 +0100	[thread overview]
Message-ID: <c1febb7b-8a79-c94b-5358-b6fb38c5a194@arm.com> (raw)
In-Reply-To: <20210817013852.3222824-4-stevensd@google.com>

On 2021-08-17 02:38, David Stevens wrote:
> From: David Stevens <stevensd@chromium.org>
> 
> Calling the iommu_dma_sync_*_for_cpu functions during unmap can cause
> two copies out of the swiotlb buffer. Do the arch sync directly in
> __iommu_dma_unmap_swiotlb instead to avoid this. This makes the call to
> iommu_dma_sync_sg_for_cpu for untrusted devices in iommu_dma_unmap_sg no
> longer necessary, so move that invocation later in the function.

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Signed-off-by: David Stevens <stevensd@chromium.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
>   drivers/iommu/dma-iommu.c | 11 ++++++-----
>   1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 8098ce593640..5dd2c517dbf5 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -504,6 +504,9 @@ static void __iommu_dma_unmap_swiotlb(struct device *dev, dma_addr_t dma_addr,
>   	if (WARN_ON(!phys))
>   		return;
>   
> +	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) && !dev_is_dma_coherent(dev))
> +		arch_sync_dma_for_cpu(phys, size, dir);
> +
>   	__iommu_dma_unmap(dev, dma_addr, size);
>   
>   	if (unlikely(is_swiotlb_buffer(phys)))
> @@ -853,8 +856,6 @@ static dma_addr_t iommu_dma_map_page(struct device *dev, struct page *page,
>   static void iommu_dma_unmap_page(struct device *dev, dma_addr_t dma_handle,
>   		size_t size, enum dma_data_direction dir, unsigned long attrs)
>   {
> -	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> -		iommu_dma_sync_single_for_cpu(dev, dma_handle, size, dir);
>   	__iommu_dma_unmap_swiotlb(dev, dma_handle, size, dir, attrs);
>   }
>   
> @@ -1062,14 +1063,14 @@ static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg,
>   	struct scatterlist *tmp;
>   	int i;
>   
> -	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> -		iommu_dma_sync_sg_for_cpu(dev, sg, nents, dir);
> -
>   	if (dev_is_untrusted(dev)) {
>   		iommu_dma_unmap_sg_swiotlb(dev, sg, nents, dir, attrs);
>   		return;
>   	}
>   
> +	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> +		iommu_dma_sync_sg_for_cpu(dev, sg, nents, dir);
> +
>   	/*
>   	 * The scatterlist segments are mapped into a single
>   	 * contiguous IOVA allocation, so this is incredibly easy.
> 

  reply	other threads:[~2021-08-19  8:59 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-17  1:38 [PATCH v6 0/7] Fixes for dma-iommu swiotlb bounce buffers David Stevens
2021-08-17  1:38 ` [PATCH v6 1/7] dma-iommu: fix sync_sg with swiotlb David Stevens
2021-08-17  1:38 ` [PATCH v6 2/7] dma-iommu: fix arch_sync_dma for map David Stevens
2021-08-19  8:59   ` Robin Murphy
2021-08-17  1:38 ` [PATCH v6 3/7] dma-iommu: skip extra sync during unmap w/swiotlb David Stevens
2021-08-19  8:59   ` Robin Murphy [this message]
2021-08-17  1:38 ` [PATCH v6 4/7] dma-iommu: fold _swiotlb helpers into callers David Stevens
2021-08-19  9:00   ` Robin Murphy
2021-08-17  1:38 ` [PATCH v6 5/7] dma-iommu: Check CONFIG_SWIOTLB more broadly David Stevens
2021-08-17  1:38 ` [PATCH v6 6/7] swiotlb: support aligned swiotlb buffers David Stevens
2021-08-17  1:38 ` [PATCH v6 7/7] dma-iommu: account for min_align_mask David Stevens
2021-08-19  9:03   ` Robin Murphy
2021-08-19 10:05     ` David Stevens

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